The present invention relates to novel block copolymers that include a random block comprised of both hydrophobic and hydrophilic monomers. Polymers of this type are useful for many different applications, including pressure sensitive adhesives as well as personal care products. The polymers are prepared by radical polymerization techniques, which can control the architecture of the polymer.
Block copolymers are known as polymers comprising molecules in which there is a linear arrangement of blocks, a block being defined as a portion of a polymer molecule in which the monomeric units have at least one constitutional or configurational feature absent from the adjacent portions. In a block copolymer, the distinguishing feature is constitutional, i.e., each of the blocks comprises units derived from a characteristic species of monomer.
A common type of block copolymer is a thermoplastic elastomer. The thermoplastic elastomers in general use contain (i) polymeric blocks (usually referred to as xe2x80x9chardxe2x80x9d blocks or A blocks) which (a) are typically amorphous and have a glass transition temperature, Tg,A, which is well above room temperature, or (b) have a crystalline polymer backbone and have a crystalline melting point, Tm,A, which is well above room temperature, and (ii) amorphous polymeric blocks (usually referred to as xe2x80x9csoftxe2x80x9d blocks or B blocks) which have a glass transition point, Tg,B, which is well below room temperature. Each soft block is linked to at least two hard blocks, so that at temperatures between Tg,B and Tm,A, or Tg,B and Tg,A, the amorphous B blocks are associated with each other, resulting in elastomeric behavior. Above Tm,A or Tg,A, melting or softening of the hard blocks permits viscous flow of the polymeric chains, resulting in thermoplastic behavior. Known thermoplastic elastomers are described for example in U.S. Pat. No. 4,260,659 (Gobran), U.S. Pat. No. 4,361,526 (Allen), U.S. Pat. No. 4,483,978 (Manser), U.S. Pat. No. 4,551,388 (Schlademan), U.S. Pat. No. 4,554,324 (Husman), U.S. Pat. No. 4,656,213 (Schladman), U.S. Pat. No. 4,764,586 (Manser), U.S. Pat. No. 4,778,852 (Futamura), U.S. Pat. No. 4,806,613 (Wardle), U.S. Pat. No. 4,919,737 (Biddle et al), U.S. Pat. No. 4,952,644 (Wardle et al), and U.S. Pat. No. 4,976,794 (Biddle et al). The disclosure of each of those patents and articles is incorporated herein by reference.
However, none of these references has prepared ABA-type block copolymers that are water or alcohol soluble. Water and/or alcohol solubility is an important property for use in commercial applications, particularly consumer applications where water and/or alcohols are considered the safest solvents. In addition, a need exists in the art of thermoplastic elastomers to make these types of polymers more accessible to different types of applications, meaning that the solubility of the polymers needs to be carefully adjusted for particular uses. For example, the water or alcohol solubility of a thermoplastic elastomer for use as a pressure sensitive adhesive will be less that the solubility of a thermoplastic elastomer for use in cosmetic or hair care applications.
In addition, graft type copolymers are generally known. Graft copolymers however, generally differ from ABA block copolymers in that the grafts are not typically attached to a terminal end portion of the middle B block. Also, the control of the architecture and chemical composition of both the backbone and grafts are usually more difficult to achieve in a graft system as compared to a multiblock copolymer.
Thus, a need exists for a water or alcohol soluble or dispersible ABA block copolymer.
This invention solves the needs by providing ABA-type block copolymer thermoplastic elastomers that have a tunable solubility in water and/or alcohols: In particular, the polymers of this invention have a block of monomers in the structure that is a random polymerized block comprised of at least two monomers, where at least one of the at least two monomers is a hydrophobic monomer and another of the at least two monomers is hydrophilic. This random block should comprise a sufficient percentage of the overall molecular weight of the block copolymer so that the solubility is adjusted in the desired manner. The hydrophobic and hydrophilic monomers are chosen, preferably, with sufficient difference in their absolute hydrophobicity (or hydrophilicity) so that copolymerization provides the tunability of the invention. In preferred methods, the absolute hydrophobicity is quantified by the absolute difference in the log P of the monomers. In other embodiments, the random block is either the A or B block.
It is another aspect of this invention to provide a method of preparing ABA-type block copolymers that comprises at least one random block by using a living-type free radical polymerization method. The living-type free radical method can be chosen from a variety of known methods, with a nitroxide radical mediated process or a radical additional fragmentation transfer (RAFT) process being particularly preferred. The living-type free radical polymerization method can be applied to formation of one or more of the blocks in the block copolymers of this invention and preferably are applied to formation of all blocks in the copolymer.
Thus, it is an object of this invention to provide a thermoplastic elastomeric polymer having an ABA-type structure with a random block to provide a desired water and/or alcohol solubility.
It is another object of this invention to provide a method of preparing thermoplastic elastomers using a free radical polymerization process, which employs living-type kinetics.
Further aspects and objects of this invention will be evident to those of skill in the art upon review of this specification.